I'm 20 and I've had my braces on for a few weeks. Definately keep soft foods in the house (mashed potatoes were my favorite). Yogurt, jello, soups, ice cream, etc.
Tell her to follow all the instructions from the orthodontist so she keeps her brackets/gums/teeth sparkling clean. Don't let her eat popcorn, sticky candies (they should give you a list of a no-go foods).
Her teeth will be sore for awhile and I've found that sugarfree gum is a life saver. It gets the blood moving and relieves some swelling. Tell her not to be afraid to chew because her teeth need to stay strong while they are moving and adjusting. AND make sure that your orthodontist gives her wax for her brackets. I'm sure the inner sides of her lips are going to be bothered by them. Roll a tiny piece of wax between your fingers and gently press it on and form it around the brackets to relieve some of that discomfort. It helped to sleep with that on for the first 3 nights or so.
I hope that helps. Good luck to her! They really aren't *that* bad.